For finer scan resolutions, the scan bar is required to move at slower speeds. Speed regulation at such low speeds presented a challenge for control. An approach successfully addressed this issue was developed. The disturbance torque in the direct current (DC) motor drive of a scan unit was calculated using the known voltage input to the motor and the measured motor speed response. The cogging torque of the motor and the friction in the mechanism can then be estimated from the calculated disturbance torque. The calculated disturbance torque was further utilized to reduce the speed ripples in speed regulation applications. A combined feedforward and feedback configuration was used to reject the disturbance based on both the offline calculated disturbance and the online estimated disturbance. This scheme was successfully implemented in consumer/commercial scan devices. Data obtained under real operating conditions demonstrated the effectiveness and robustness of this disturbance compensation scheme.

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